In the prior art, various attempts have been made at realizing biocompatible and flexible sensors and electronics. Thin film transistors (TFTs) on various flexible substrates have been reported including organic TFTs, Si TFTs, carbon nanotube (CNT) and graphene FETs on polymer substrates, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide. However, the TFTs in the prior art have limited in vivo lifetime due to foreign body reactions in cells, such as fibrotic encapsulation or glial scarring, and also cause inflammation.
Graphene transistors having potential application for a cellular interface are described in “Graphene and nanowire transistors for cellular interfaces and electrical recording”, Nano Letters 10, 1098 (2010). These graphene transistors are fabricated on an oxidized Si substrate with mechanically exfoliated graphene flakes using e-beam lithography. However, mechanically exfoliated graphene is not compatible with a micro-fabrication process, and it is not scalable. Further, the oxidized Si substrate described can damage tissues and nerves, which is a significant limitation against in vivo applications.
Solution-gated graphene transistors on an insulating rigid substrate are described in “Graphene transistors for bioelectronics”, Proceed. of the IEEE 101, 1780 (2013). However, graphene transistors fabricated on a rigid surface are not well suited for in vivo use.
Transistors formed on a microbial cellulose substrate are described in “Biocellulose based materials for organic field effect transistors”, Pro EUROCON and CONFTELE 2011, Lisbon, Portugal, and “Bacterial cellulose as substrate for inkjet printing on organic thin film transistors”, ICOE 2012 Abstract. These two papers describe Pentacene- and RR-P3HT (regioregular poly(3-hexylthiophene)-based organic thin film transistors (OTFT) fabricated on a bacterial cellulose (i.e, microbial cellulose) film. Pentacene and RR-P3HT are organic semiconductors, which typically have very low carrier mobility (<5 cm2/Vs). The FET mobility of the pentacene and RR-P3HT transistors on the bacterial cellulose are reported to be 0.0033 cm2/Vs, and 0.057 cm2/Vs, respectively. Due to the low carrier mobility, the pentacene and RR-P3HT transistors need to be operated with a high drain voltage (a few tens of volts) and a high gate potential (a few tens of volts). The slow speed and the high dissipation power are the major limitations to bioelectronics applications.
What is needed are biocompatible and flexible sensors and electronics that do not have these limitations. The embodiments of the present disclosure answer these and other needs.